This invention relates generally to a guide rail assembly for supporting a vehicle seat and more specifically, it relates to a guide rail assembly of the type which includes at least two pairs of mutually engaging rails arranged respectively at lateral sides of the vehicle seat, one rail being secured to the seat and having mounting means for a safety belt, and the other rail being secured to the floor of the vehicle.
In contemporary designs of motor vehicles, the trend is to anchor safety belts directly on the seat and not on the body of the vehicle. Conventionally, the safety belts have a V-shaped structure defining a shoulder belt portion and a lower belt portion stretching over the lower part of the abdomen. The apex of the V-shaped belts is terminated with a buckle plug directed to the inner lateral side of the seat and insertable into a buckle socket secured to the inner side of the vehicle seat. By means of this arrangement it is assured that the position of the safety belt is substantially independent from the position of the vehicle seat so that irrespective of the adjustment of the seat position by short or tall persons, the position of the safety belt relative to the seat remains always the same and the safety belt can be used under most favorable conditions.
In this arrangement of safety belts, it is required that at least one pair of cooperating guide rails in the guide rail assembly be designed such that even in the case of an accident, especially in the case of a frontal or impact collision, the resulting inertial forces occurring during the abrupt acceleration or deceleration of persons using the seat, be transmitted from the guide rail assembly to the floor of the vehicle. Especially at a head-on collision of the motor vehicle, the safety belts secured to the seat overload the guide rail assembly supporting the seat particularly in the vertical direction. Consequently, it may happen in the course of such an accident that the interlacing rails are torn apart (separated) in the manner of a zipper and consequently, the user of the vehicle seat may suffer a serious unjury.
In conventional guide rail assemblies, the two interlaced guide rails have upwardly directed U-shaped sections, the shorter arms of which overlap each other. These U-shaped regions of the rails have a slim configuration whereby the short arms of respective rails engage each other in a mirror-like fashion and project almost entirely into the recess formed by the U-shaped end portion of the cooperating rail. By virtue of this slim profile the two rails engage each other over a relatively large vertical section. As a consequence, very high bending moments can be intercepted in vertical direction and the aforementioned tearing-off in a zipper-like manner is effectively prevented. Also the mirror-symmetrical hooking of the two rails contributes to the resistance of the guide rail assembly inasmuch as one rail is hooked up into the other to the same degree.
Nonetheless, the study of accidents and experiments have prooved that even in the conventional vertically oriented engaging pairs of guide rails, the possibility still exists that the two engaging rails can be torn apart from one another. Especially the engaged pair of guide rails situated near the central plane of the motor vehicle is susceptible to a rupture beginning at the rear end of the line of their engagement. To avoid this possibility it has been devised to dimension the material of the profiled rails such that forces of the strength up to 40 KN for example, that means up to 40,000 kg/m-sec.sup.2 be absorbed without tearing apart the individual rails from the cooperating guide rails. By these measures, however, the weight of each rail pair is increased in a very disadvantageous manner.